1. Field of the Invention
The present invention relates to a field emission device. More specifically, the present invention relates to a field emission device having a cathode structure for stable field emission.
2. Discussion of Related Art
In a typical field emission device, cathodes are separated from each other at adequate intervals for electrical disconnection on a plane, and field emitters, such as carbon nanotubes, are formed on the separated electrodes.
FIG. 1 is a cross-sectional view of a conventional field emission device having a plurality of cathodes, FIG. 2 shows how charges accumulate on an insulator of the field emission device of FIG. 1, and FIG. 3 shows abnormal field emission due to accumulated charges.
As shown in FIG. 1, a plurality of cathodes 110 are arranged separated from each other on a cathode substrate 100 facing an anode substrate 150 and an anode 160. A field emitter 120 is formed on each cathode 110. In a space 121 between the separated cathodes 110, charges may accumulate on the cathode substrate 100, which is like an uncovered area of a glass substrate and is an insulator when field emission is performed at a high voltage as shown in FIG. 2. In other words, electrons 171 are normally emitted and accelerated by an electric field formed by the voltage supplied to the anode 160. However, some electrons 172 may abnormally scatter, and the glass substrate 100 hit by the electrons 172 may generate secondary electrons 173 and positive ions 174.
If the positive ions 174, which are located in the space between the anode substrate 150 and the cathode substrate 100, accumulate in the space 121 between the cathodes 110, the amount of charges gradually increases because the insulated cathode substrate 100 is unable to transmit the accumulated charges, which results in abnormal operation.
As shown in FIG. 3, in addition to a normal electric field E formed by the anode 160 inducing electrons from the field emitter 120, an electric field Echarge is formed by positive charges 175 between the insulated cathodes 110. This causes abnormal field emission.
Since the amount of the accumulated charges 175 varies over time and the surface condition of an insulated area where there is no electrode, it is difficult to control the amount of accumulated charges 175. Moreover, if too many charges accumulate over time for the insulated cathode substrate 100 to accommodate, the accumulated charges will suddenly discharge to the adjacent cathode 110. Such an arc discharge phenomenon is a very dangerous factor affecting the stability of the field emission device.
If the density of the field emitters on the cathodes is increased without considering abnormal operation of the field emission device due to charge accumulation, a variety of problems may occur. The present invention provides a method for overcoming abnormal operation due to the above causes.